Method of and means for measuring the depth of penetration of bullets within subsurface formations



July 27, 1954 RECOROEfl R. L. HOSS METHOD OF AND MEANS FOR MEASURING THEDEPTH OF PENETRATION 0F BULLETS WITHIN SUBSURFACE FORMATIONS Filed May8, 1951 Robert L. Hosa- INVENTOR. I

Patented July 27, 1954 METHOD OF AND ME THE DEPTH OF P LETS WITHIN SUBANS FOR MEASURING ENETRATION OF BUL- SURFACE FORMATION S Robert L. Hoss,Corpus Christi, Tex. Application May 8, 1951, Serial No. 225,164 10Claims. (Cl. 250-83.6)

This invention relates to new and useful improvements in methods of andmeans for measur ing the depth of penetration of bullets withinsub-surface formations.

As is well known, gun-perforating of well casing or pipe is generalpractice and the usual gunperforating operation involves the perforationof the casing by firing a selected number of projectiles or bulletsthrough the wall of the casing in radial directions from the well bore.The bullets penetrate the well casing and the cement which cements saidcasing in place and enter the subsurface formation to thereby establishcommunication between the formation and the well bore. Although it hasbeen heretofore recognized that the depth of penetration into thformation by the projectile or bullet affects the subsequentproductivity of the formation, there is now no known satisfactory methodfor accurately determining the distance which the bullet has penetratedthe formation.

In gun-perforating, the operator generally selects the particular sizegun, the specific size bullet and the volume of the charge to be used inaccordance with his past experience with the type of formation and inaccordance with the size of the casing to be perforated so that actuallythe selection of the essential factors is on a more or less guessworkbasis. After completion of the gun perforating operation, there is noway of knowing whether proper depth of penetration has been obtained.Even in those cases where the well produces after the gun-perforatingoperation, the operator is without knowledge that proper depth ofpenetration, which would provide maximum productivity, has beenaccomplished. In those instances, where no productivity is hadsubsequent to the perforating operation, it has been assumed that theformation is non-productive when, in fact, such non-productivity mayhave been due to failure of the bullets to properly penetrate into theformation or to properly perforate the casing and cement walltherearound.

It is, therefore, one object of this invention to provide an improvedmethod for accurately determining the depth of penetration of aprojectile or bullet which has been fired into a sub-surface formationby a perforating operation, whereby positive knowledge as to said depthof penetration is obtained.

An important object of the invention is to provide an improved method ofdetermining the depth of penetration of a projectile into a subsurfaceformation wherein a controlled amount of radioactive material isincorporated within the projectile so that said projectile emanatesradioactive radiations of a predetermined intensity at a known distance,and thereafter determining the depth of penetration of said projectileby measuring the intensity of the radiations at a point within the wellbore.

Another object is to provide a method, of the character described,wherein the intensity measi urements are made in only a singlehorizontal plane Within the well bore, whereby accurate determination ofthe depth of penetration of each projectile may be accomplished eventhough the projectiles are relatively close to each other in horizontalplanes.

F each projectile, and visibly recording the measurements at thesurface.

A further object is to provide an improved apparatus for determining thedepth of penetration of a projectile within a sub-surface formation andincluding, a Geiger-Muller counter or ionization chamber which isshielded in a manner to receive radiations in only a single restrictedhorizontal plane.

The construction designed to carry out the invention will be hereinafterdescribed together with other features thereof.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, wherein an example of the invention is shown,and wherein:

Figure 1 is a sectional view of a well bore illustrating the projectileswithin the sub-surface formation and showing the detecting instrumentlowered within said bore,

Figure 2 is a horizontal cross-sectional view taken on the line 2-2 ofFigure 1,

Figure 3 is a sectional detail of a gun barrel assembly having aprojectile which is employed in carrying out the method mounted therein,and

Figure 4 is an enlarged view of the indicating chart which records themeasurements.

In the drawings thenumeral I0 designates a well bore having a wellcasing or pipe H extending therethrough. In accordance with the a w M-etthe projectiles or bullets usual practice the well casing is cemented inplace by cement [2.

As has been noted, it is the usual practice to employ a gun perforatorwhich fires projectiles or bullets through the wall of the casing l lthrough the cement and into the sub-surface area or formationsurrounding the well bore. It has been recognized that proper depth ofpenetration by must be accomplished in order to obtain maximumproductivity from the formation but heretofore there has been no methodfor ascertaining whether or not proper penetration of the projectiles orbullets into the formation has been accomplished.

In carrying out the present invention, each projectile or bullet A maycontain a known controlled quantity of radioactive material whereby saidprojectile or bullet will emanate radioactive radiations of a givenintensity. All of the projectiles or bullets are constructed in anidentical manner, that is, each of said projectiles containsubstantially the same quantity of radioactive material, which meansthat all bullets emit radioactive radiations of the same intensity atthe same distance. The particular construction of each projectile A issubject to variation and so long as said projectile contains apredetermined or measured quantity of the radioactive material, thepurposes of the present invention may be accomplished. As illustrated inFigure 3, the projectile comprises the usual bullet l3 mounted withinthe bore of the gun barrel i l and said barrel housing Ida has the usualpowder chamber l4b behind the bullet; the powder is ignited in any wellknown manner by the igniter cord Me. This is typical gun barrel assemblyand forms no part of the present invention since any suitable gunperforator may be employed for pro jecting the bullet.

The body of the bullet contains the radioactive material it which may beradioactive salt, uraninite or any other material capable of emittingradioactive radiations, and said material may be disposed within thebody of the bullet in any convenient manner. As shown, the bullet isbored out and the radioactive material is disposed within a capsulewhich is retained within the bore by a threaded closure I511.

When the casing II is to be perforated the gun perforator (not shown) isloaded with the projectiles A, each of which has embodied there in thecontrolled or known quantity of radioactive material l5. The gunperforator is then lowered into the well here and actuated in the usualmanner to fire the projectiles through the wall of the casing H in aradial direction and thereby perforate said casing. In Figure l, theprojectiles Al, A2, A3 and AA have been illustrated as having differentdepths of penetration and said projectiles horizontal planes orelevations. As shown, the lowermost projectile A! has penetrated aconsiderable distance into the sub-surface formation F, while theprojectile A2 has not penetrated through the cement wall between thecasing ii and the well bore. The projectiles A3 and Ad have penetratedthe cement but their depth of penetration into the formation isdissimilar.

In order to determine the depth of penetration of the projectiles themeasuring instrument B is lowered within the well bore by means of theusual conductor cable IS. The instrument includes a housing l! which iscentered within the well casing H by the usual bowed centralizer springsl8. Mounted within the lower portion of are disposed in different ell)the housing is a Geiger-Muller counter or ionization chamber [9, and asis well known, this counter is responsive to radioactive emissions. Inorder to cause the counter to receive the radioactive emissions in onlya single horizontal plane, the counter or ionization chamber is shieldedby suitable lead sleeves or collars 28 and 2| which are interposedbetween the chamber l9 and the housing I1. The shielding collars orsleeves are suitably secured within the housing ll and are spaced apartfrom each other to provide an annular entry slot 22 through whichradiations originating from a source in the same plane as the plane inwhich said slot is located may be received. The upper end of theconductor cable I6 has electrical connection with any well knownrecording device which recordsv the measurements made by the Geigercounter [9.

Usually the instrument B is lowered to a point below all projectiles andis then moved upwardly; during such upward movement the instrument isoperated to make the desired measurements. As the instrument B is raisedwithin the well casing, the movement of the entry slot 22 in the lowerportion of the instrument opposite the lowermost projectile Al willcause the radiation originating from the projectile Al to enter saidslot and be received within the ionization chamber 1 9. Due to theshielding by the members 20 and 2|, any radiation from the next adjacentprojectile A2 will not affect the counter, and therefore, the operationof the counter will be controlled solely by the radiations of theprojectile opposite or in the same horizontal plane as the entry slot22. Because of the centralizing springs 18, the counter it will bemaintained at substantially the axial center of the well bore.

The magnitude of the current flowing through the center wire of theionization chamber [9 is inversely proportional to the square of thedistance that the particular radioactive projectile is located from saidionization chamber. In other words, the intensity of radiation from theprojectile Al at the center of the well bore where the Geiger counter islocated is determined by the distance of the projectile from thecounter, and this distance is obviously dependent upon the depth ofpenetration of said projectile. Therefore, the counter actually measuresthe intensity of the radiation from the projectile Al and thismeasurement may be converted into a visible reading representative ofdepth of penetration by means of the usual recording chart and stylus.

When the instrument B is moved upwardly to locate the entry slot 22 inthe same plane as the second projectile A2, the counter 19 is responsive to the radiations emanating from this projectile. Asillustrated, this projectile has not penetrated the cement and istherefore much closer to the axial center of the well bore or closer tothe Geiger counter than was the projectile Al. Since the projectile A2contains the same quantity of radioactive material as does theprojectile Al it willbe evident that the intensity of the radiationsreceived by the counter I 9 from projectile A2 will be considerablygreater than the radiations previously received from the further removedprojectile Al. This difference in intensity which is actually measuredby the counter will, of course, be recorded and indicated at thesurface. It is noted that because of the shielding arrangement thecounter I9 will be shielded from any extraneous radiation from either ofthe adjacent projectiles AI and A3. In

this regard, it might be noted that inugun perforating the difference inelevation between projectiles may be a matter of inches, and thereforeit is important that the counter or ionization chamber be properlyshielded to receive the radiations from only one projectile at any onetime.

As raising of the instrument is continued, the entry slot 22 of saidinstrument is moved opposite the projectile A3 to measure the intensityof the radiations therefrom and is thereafter raised opposite theprojectile A4 to measure intensity of radiation from this lowermostprojectile. Although four projectiles are illustrated in Figure 1, anydesired number may be projected through the wall of thecasing and theintensity of the radiation of each will be measured in turn as theinstrument is raised past said projectiles. Because all of theprojectiles contain the same quantity of radioactive material andbecause the intensity of the radiation of each projectile varies inaccordance with its distance from the ionization chamber, it is evidentthat an accurate determination of the depth of penetration of eachprojectile may be made.

The particular recording mechanism 23 which is located at the surfaceis, as has been stated, subject to variation. However, it is preferableto employ the well known recording chart and stylus arrangement, and inFigure 4, a view of the chart 24 is illustrated. The length of the chartis representative of the depth of the instrument and the chart will bedriven in synchronization to the lowering and raising of the cable 16.The transverse width of the chart may be calibrated in distancerepresentative of depth of penetration. The recording or indicating line25 is made by a suitable stylus which is controlled by the operation ofthe Geiger counter as the latter measures the intensity of theradiations emitted by the various projectiles. As illustrated in thechart, the initial oiTset 26 in the recording line 25 is indicative ofthe depth of penetration of the first projectile Al. Because theprojectile Al is a considerable distance from the counter I9, the offset26 is relatively small since the intensity of radiation at the point ofreception is not too great.

The second offset 21 illustrated on the chart is representative of thedepth of penetration of the projectile A2, and since this projectile hasnot penetrated the cement wall the intensity measurement is quite highthereby resulting in a relatively large-offset in the indicating line25. The offset 28 on the chart is indicative of the depth of penetrationof the projectile A3 and this penetration, although through the cementwall I2, is not too deep into the sub-surface formation F. The offset 29on the chart is representative of the depth of penetration of theprojectile A4 which has entered the formation about the same dis tanceas projectile Al.

From the foregoing it will be evident that a simple and accurate methodand apparatus for measuring the depth of penetration of projectiles isprovided. Each projectile has incorporated therein a predetermined knownor measured quantity of radioactive material with the result that if allprojectiles were exactly the same distance from the counter orionization chamber IS, the intensity measurements made by said counterwould be identical. With this arrangement the variation in distancebetween each projectile and the counter results in a variation inintensity which is inversely proportional to the square of e thedistance and the intensity measurements made by the counter are ameasure of said distance. This intensity measurement is transposed intoa visible record calibrated in depth of penetration and providesaccurate knowledge as to the exact distance which each projectile hasbeen projected into the sub-surface formation. The shielding of thecounter or ionization chamber IS in a manner to permit reception ofradiations inonly a single horizontal plane is important because in gunperforating the projectiles are relatively close to each other withrespect to horizontal elevations or planes; as a matter of fact, it isnot uncommon for the projectiles to be fired within four to six inchesof each other in different horizontal planes and in order to permitaccurate determination the counter or ionization chamber must beshielded against the effects of any radiation other than that from theparticular projectile being investigated. It is also important to thepresent invention that the counter or ionization chamber be maintainedin the same relative position within the well bore throughout themeasurements made with respect to all of the projectiles, since thisassures that any variation in distance between the counter and theprojectile. is due solely to the difference in the depth of penetrationof each projectile as compared to the other projectiles.

It is pointed out that the radiation from the radioactive projectile isof such a high order of magnitude as compared to the intensity ofnatural earth radiation that natural radiation will not be recorded onthe penetration record. The particular measuring instrument B isconstructed to be substantially insensitive to natural radiation wherebywhen said instrument is at any point in the well bore other thanopposite the projectiles the stylus forms the substantially straightline 25 on the indicating chart.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction may be made, within the scope of the claims, withoutdeparting from the spirit of the invention.

I claim:

1. The method of determining the depth of penetration of projectilesinto a sub-surface area surrounding a well bore including, depositing aplurality of projectiles each having identical radio ctive radiationemitting qualities into the su -surface area at different elevationstherein, and thereafter measuring the intensity of the radiationsemanating from each projectile in situ within the sub-surface area.

2. The method of determining the depth of penetration of projectilesinto a sub-surface area surrounding a well bore including, depositing aplurality of projectiles each having identical radioactive radiationemitting qualities into the sub-surface area at different elevationstherein, moving an instrument responsive to radioactive radiationswithin the well bore, and maintaining the instrument in the sameposition in a vertical plane Within the bore throughout its movementtherethrough, and measuring by means of said instrument the intensity ofthe radiations emanating from each projectile, which intensity is ameasure of the depth of penetration of said projectile.

3. The method as set forth in claim 2, together with the step ofshielding the instrument from all radiations 'other than those from theprojectile oppositezsaid measuring instrument.

4. The method of determining the depth of penetration of a plurality ofprojectiles into a subsurface area surrounding a v@ bore including,depositing the projectiles at various horizontal elevations in thesub-surface area, each projectile having the same predetermined quantityof radioactive material therein whereby said projectiles emitradioactive radiations, thereafter measuring the intensity of theradiations emanating from each projectile in situ within the sub-surfacearea, and transposing at the surface the measurements so made intovisible indications of depth of penetration of each projectile into thesub-surface area.

5. The method of determining the depth of penetration of proj tiles intoa sub-surface area surrounding a W l bore including, introducing intoeach projectile a measured quantity of radioactive material, thereafterdepositing the projectiles into the sub-surface area at differentelevations therein, and thereafter measuring the intensity of theradiations emanating from each projectile in situ within the sub-surfacearea.

6. The method of determining the depth of penetration of proje iles intoa sub-surface area surrounding a w bore including, introducing into eachprojectile a measured quantity of radioactive material, thereafterdepositing the projectiles into the sub-surface area at differentelevations therein, thereafter successively receiving radiationsemanating from each projectile at a predetermined point within the wellbore, and measuring the intensity of the radiations received from eachprojectile, the reception point being successively varied in ahorizontal plane to receive emanations from all projectiles but beingmaintained constant in a vertical plane with respect to the axis of thewell bore.

7. The method of etermining the depth of penetration of projecxges intoa sub-surface area surrounding a wel' bore including, introducing ameasured quantity of radioactive material into each projectile so thatall projectiles contain the same quantity, thereafter firing theprojectiles into the sub-surface area at diiferent horizontal elevationstherein, moving a measuring instrument responsive to radioactiveradiations within the well bore while maintaining the instrument in thesame vertical plane with respect to the axis of the bore to cause saidinstrument to successively move past each projectile, and measuring bymeans of the instrument the intensity of the radiations emanating fromeach projectile, which intensity is a measure of the depth ofpenetration of said projectile.

8. The method as set forth in claim 1,.together with the step ofshielding the measuring instrument from all extraneous radiations otherthan those from the particular projective opposite said measuringinstrument in a horizontal plane.

9. An apparatus for determining the depth of penetration of a projectileinto a sub-surface formation-surrounding a well bore including, aprojectile having a measured quantity of radioactive materialincorporated therein, and an instrument adapted to be lowered throughthe well bore and responsive to radioactive radiations, and means withinsaid instrument for measuring the intensity of the radioactiveradiations emanating from the projectile after said projectile has beendeposited within the subsurface formation.

10. An apparatus for determining the depth of penetration of aprojectile into a sub-surface formation surrounding a well boreincluding, a prgFotfle having a measured quantity of radioac ve materialincorporated therein, an instrument adapted to be lowered through thewell bore and responsive to radioactive radiations, means within saidinstrument for measuring the intensity of the radioactive radiationsemanating from the projectile after said projectile has been depositedwithin the sub-surface formation, and electrically operated recordingmeans at the surface of the well bore and electrically connected withthe instrument for transposing the intensity measurements into a visibleindication of the depth of penetration of the projectile into theformation.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,228,623 Ennis Jan. 14, 1941 2,469 161 Russell May 10, 19492,508,772 Pontecorvo May 23, 1950 2,515,535 Thayer et a1. July 18, 1950OTHER REFERENCES Radioactivity Well Logging," by E. N. Tiratsoo,reprinted from Petroleum, published by Leonard Hill, Ltd, Jan. 1948, 6pages.

